Functional surfactants as energy valves in gradient structures of organic inorganic perovskite structures

Abstract

Hybrid perovskites are considered one of the most promising semiconductor materials of our time. Their ionic composition enables low-cost and simple production at low temperatures, making them a highly demanded semiconductor for photovoltaics, but also optoelectronic applications such as LEDs, lasers or photodiodes. Their hybrid nature enables the integration of organic cations, which brings a wide range of possible materials. The classical perovskite structure permits the incorporation of small organic cations. If the given space in the structure is exceeded by the organic molecule, a layered crystalline phase with alternating arrangement of organic cations and inorganic 2D lead bromide layers is formed. This allows the use of a great variety of organic cations which become an integral part of the semiconducting material. Thus, molecules can be chosen that contribute to the functionality of the crystalline phase, for example, by using conductive conjugated π systems. Energy transfer between the components of the layered phases becomes possible and extraordinary electronic and optical properties can result. The aim of this thesis was the development of functional surfactants for the synthesis of hybrid lead halide perovskite particles with a special switchable feature. The switching was intended to introduce an energy valve into the phases, which could be switched by external stimuli (i.e. light or chemically). The obtained phases should be investigated for structural, optical and electronic properties, both before and after a switching of the ligands. For this purpose, ligands based on photoswitchable azobenzene, redox active ferrocene and conductive five-ring heterocycles were developed and their functionality was studied before and after incorporation into 2D layered hybrid perovskite phases. It was found that electronic exchange between the organic molecule and the perovskite framework is present in all the crystal phases obtained. Thus, the molecules are more than just a structural component of the phases, but contribute to the electronic properties. The oxidation of ferrocene in particular made it possible to integrate a switchable energy valve. The decisive factor is the change in the energy of the molecular orbitals, which was achieved by the oxidation. Thus, the optical and electronic properties of the semiconductor could be greatly changed. This work provides a comprehensive basis for the study of semiconducting particles with switchable ligands. Especially promising are redox-active hybrid perovskites, which emerge as a completely new class from these investigations.